This section provides background information related to the present disclosure which is not necessarily prior art.
Conventionally, the three-phase motor is driven by three sinusoidally varying AC currents phased 120 degrees apart. Many modern designs produce these AC currents using pulse-width modulated (PWM) direct current. The PWM drive waveforms are generated by a software controlled microprocessor whose PWM outputs are fed to an H-bridge switching circuit that essentially connects and disconnects each of the three-phase motor coils to a source of DC current (modulated by PWM to simulate sine wave).
The problem with the conventional PWM design is that there are cyclically occurring instances where the respective coil windings are shorted to each other. While this does not affect the simulated sinusoidal waveforms, it can cause problems. Motor coil windings are essentially inductors, and inductors store electromagnetic energy. When the coil windings are shorted together, the stored electromagnetic energy will inevitably find a leakage path and this can cause spurious leakage currents that adversely affect the microprocessor and the associated power supply components. In some cases these leakage currents are even sufficient to trip the ground fault interrupter (GFI) circuit associated with the power supply components.